Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Loss (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	$ (5,676)	$ (2,533)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(76)	(28)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	281	92
Net current-period other comprehensive income (loss)	205	64
Ending balance	(5,471)	(2,469)
UnrealizedGainsLossesFromDefinedBenefitPensionAndPostretirementPlanItems [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	(5,643)	(2,533)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	248	92
Net current-period other comprehensive income (loss)	248	92
Ending balance	(5,395)	(2,441)
Accumulated (Gain) Loss from Commodity Contracts Cash Flows Hedges [Member]
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Roll Forward]
Beginning balance	(33)	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(76)	(28)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	33	0
Net current-period other comprehensive income (loss)	(43)	(28)
Ending balance	$ (76)	$ (28)